Implicit isomorphisms with ScalaZ

ImplicitIsos.scala

import scalaz.Isomorphism.<=>

/** Our example Isomorphism */
trait StringIntIso {

  implicit object StringIntIso extends (String <=> Int) {
    override val to: (String) => Int = _.toInt
    override val from: (Int) => String = _.toString
  }

}

/** This will not behave as expected */
trait ImplicitIsomorphismsFail {
  implicit def impliedTo[A, B](a: A)(implicit iso: A <=> B): B = iso.to(a)
  implicit def impliedFrom[A, B](b: B)(implicit iso: A <=> B): A = iso.from(b)
}

trait ImplicitIsomorphismsSuccess {
  /** We only need one direction due to [[scalaz.Isomorphism.isoCommutative]] */
  implicit def impliedIso[A, B](a: A)(implicit iso: A <=> B): B = iso.to(a)
}

object Foo extends ImplicitIsomorphismsFail with StringIntIso {
  // Do not compile
  // val x: StringValue = "asdf"
  // val y: String = x
}

object Bar extends ImplicitIsomorphismsSuccess with StringIntIso {
  val x: Int = "asdf" 
  val y: String = x
}

object BarDesugar extends ImplicitIsomorphismsSuccess with StringIntIso {
  val x: Int = BarDesugar.impliedIso("asdf")(BarDesugar.StringIntIso)
  val y: String = BarDesugar.impliedIso(BarDesugar.x)(scalaz.Isomorphism.isoCommutative)
}